D15B with Neptune RTP

[oil pan 4]

How lean can we go before we start to burn valves?

[EggyD]

Well there's a guy on d-series.org with a del sol that's getting over 70 mpg and his tune is over 22 afr with no ill effect. I figured I was safe at 19 with timing advanced to 45 degrees. So fare I've gotten over 2000 miles on this setup and all is good. (knock on wood)

[mwebb]

Originally Posted by oil pan 4

How lean can we go before we start to burn valves?

slightly lean is the problem
very lean results in reduced combustion temps

look at a 5 gas graph for nox , nox forms at high combustion temps
look where the peak for nox is .

[mwebb]

Originally Posted by Tygen1

I wouldn't split hairs on exahust pipe size. While I'm sure it could be optimized for FE, I don't expect that to be the need in this case. I have an oversized exhaust pipe as well. I like to use my car for more than just good FE. Even when I go drag racing, I am still getting great FE I want my cake, with frosting and I want to eat it too! Lean Burn is the frosting

the rpm you want to optimize performance at
there is only one correct answer

you get to choose - but a gain at one rpm is going to be a
UN gain at the other end of the spectrum

[oil pan 4]

What I have read is 13.2:1 produces the most torque and "highest" EGT's.
But I don't know if that is highest EGTs of all A/F ratios or the highest you get using normal ratios such as 12:1 through 15:1.

I googles searced for quite a while last night and could not find a magic number for the exhaust valve burning air:fuel.
I have burned exhaust valves before I had a car where the IAT sensor was reading 300'F on a normal 70'F day, caused it a nasty lean condition and burned the valves on every cylinder.
Never thought to look for peak NOx to find the highest EGT mixture. I bet that will work.
If I find anything I will post it here. Burning out your exhaust valves to save gas isn't going to save us any money.

An expensive alternative could be to get Sodium core inconel 625 exhaust valves. They are burn proof. I know you can get them for pretty much any chevy V8 gas engine ever made, not sure about getting them for 4 cylinders.

[oil pan 4]

Computerized Engine Controls - Google Books
What air fuel ratio burns valves?
What air fuel ratio causes the most NOx to form?
Looks like just short of 16:1 is your peak for NOx production and likely the peak for combustion flame temperature.
But once you pass 16:1 NOx levels start to drop quickly. 16.5:1 looks about as NOx-ious as 14.7:1.

[Tygen1]

Oil Pan, we are only use these lean conditions under light loads. In your case, you were accelerating under heavy loads while lean, that's why you burned valves.
At some point, I would like to put a EGT gauge in my car to confirm a drop in combustion tempature.

[oil pan 4]

Yes my car was running lean all the time.
You can score a new EGT off ebay for cheap like I did. Or get a used one real cheap if you want to get creative.

[mwebb]

..."I have burned exhaust valves before I had a car where the IAT sensor was reading 300'F on a normal 70'F day, caused it a nasty lean condition and burned the valves on every cylinder."...

FALSEly hi IAT values will cause
retarded Ignition timing
which will change the timing of Peak Combustion Pressure to
After 14 degrees atdc ...
so part of the charge burns in the exhaust
not in the combustion chamber

contributing to
burnt exhaust valves

[oil pan 4]

The car had a mechanical ignition system timing with mechanical and vacuum advances.